The invention is an improvement over inventions described in U.S. Pat. No. 5,361,642 to Charles R. Welch, entitled the Column-Based Stress Gage, which issued Nov. 8, 1994, and U.S. Pat. No. 5,447,065 to Charles R. Welch et al., entitled High-Fidelity Particle Velocity Gage For Measuring Strong Motions in a Solid Media which issued Sep. 5, 1995, the teachings of which are incorporated herein by reference. The patents are commonly assigned to the United States of America.
One method to measure normal stress and velocity at a given location in a material uses the two instruments described in the above noted patents separately. In the method, the column-based stress gauge and the high-fidelity velocity gauge are placed independently, sometimes in pairs, with each instrument physically separated from the other instrument. Because the stress and velocity measurements are best interpreted as pairs of measurements, the physical separation of the instruments increases the complexity of the data interpretation, which increases the chances of interpretation errors. The separate placement for each instrument also increases the possibility of errors in the coupling between the pair of instruments and the surrounding medium, and this consequently increases the likelihood of errors in data interpretation.
Another method of measuring normal stress and material velocity at nearly the same location is to use some of the other types of stress and velocity gauges in existence and combine these in a single package. These other stress and velocity instruments lack the advantages of the aforementioned patents. In addition, in some cases, the external shape of so-called velocity gauges used in these other methods compromise normal stress measurements made in proximity to such velocity canisters.